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Light Reflection and Refraction
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12/08/2021 1:16 pm
Topic starter
At what distance from a concave mirror of focal length 10 cm should an object be placed so that:
(a) its real image is formed 20 cm from the mirror?
(b) its virtual image is formed 20 cm from the mirror?
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12/08/2021 1:24 pm
(a) f = -10 cm
v = -20 cm (real image)
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{-20}\) + \(\frac{1}{u}\) = \(\frac{1}{-10}\)
\(\frac{1}{u}\) = \(\frac{-1}{10}\) + \(\frac{1}{20}\)
= \(\frac{-1}{20}\)
u = -20 cm
(b) f = -10 cm
v= 20 cm (virtual image)
\(\frac{1}{v}\) + \(\frac{1}{u}\) = \(\frac{1}{f}\)
\(\frac{1}{20}\) + \(\frac{1}{u}\) = \(\frac{1}{-10}\)
\(\frac{1}{u}\) = \(\frac{-1}{10}\) + \(\frac{-1}{20}\)
= \(\frac{-3}{20}\)
u = -\(\frac{20}{3}\)cm